Remove plugins before copying them again.

This way plugins can rename/delete files w/o having old files lying around.
Only delete core plugins.
Use PLUGIN_PATH in dokku default case.
contrib: add dokku client shell script

This is adapted from the one I use in my shell profile scripts. This
kinda-sorta-maybe acts like the `heroku` or `deis` commands and does
some clever reorganization of data before sending it to the server.

To use the app name generator, install the `elfs` rock from Moonrocks.
port 'wait_to_retire' from broadly/dokku
Actually suppress the output from the git commands
Merge remote-tracking branch 'upstream/master' into mh-merge-upstream
Merge pull request #1 from expa/mh-merge-upstream

merge from upstream
Update vagrant installation instructions

Avoids 
```
Permission denied (publickey).
fatal: The remote end hung up unexpectedly
```
that can occur on certain Vagrant images. Since we need readonly anyway, might as well use HTTPS instead of SSH.
Merge pull request #735 from andrewsomething/master

Redirect to the app deployment docs on success.
Update README.md

Sorry, that typo was getting to me :)
Merge pull request #745 from rcarmo/patch-1

Update README.md
replace gitreceive by sshcommand in example url
fix dokku development blog link

http://progrium.com/dokku doesn't exist anymore. The blog is really at http://progrium.com/blog, but http://progrium.com is by default on the blog, so let's use this link.
Merge pull request #748 from vincentfretin/patch-2

fix dokku development blog link
The app certificates directory was renamed to tls in e2135a2c5f599184ce1f40beb21fccb9a0f8b8de
Remove unintended phrase repetition in installation.md.
Merge pull request #750 from th4t/master

Remove unintended phrase repetition in installation.md
Merge pull request #746 from vincentfretin/patch-1

replace gitreceive by sshcommand in example url
Merge pull request #749 from vincentfretin/master

Fix app certificate directory in backup-import/export